Preheat your oven to 400°F (200°C). Place the peeled and cubed sweet potatoes on a large baking sheet, drizzle lightly with olive oil, and roast for 30–35 minutes until fork-tender and slightly caramelized at the edges. Alternatively, you can boil the sweet potatoes in salted water for 15–20 minutes until very tender, then drain well.

Reduce oven temperature to 350°F (175°C). Grease a 9x13-inch baking dish (or equivalent 3-quart casserole dish) with butter or cooking spray and set aside.

Transfer the cooked sweet potatoes to a large mixing bowl. Using a hand masher, potato ricer, or electric hand mixer on low speed, mash until completely smooth and creamy.

Add the softened butter, maple syrup, milk or cream, beaten eggs, vanilla extract, cinnamon, nutmeg, and sea salt. Mix together until fully combined and silky smooth. Taste and adjust sweetness or spice as desired.

Spread the sweet potato filling evenly into the prepared baking dish, smoothing the top with a spatula.

In a medium bowl, combine the roughly chopped pecans, brown sugar, melted butter, flour, cinnamon, and salt. Stir together with a fork until the mixture resembles a chunky, clumping crumble.

Sprinkle the pecan topping evenly over the sweet potato filling, distributing it all the way to the edges of the dish.

Bake at 350°F for 25–30 minutes, until the topping is golden brown and crisp and the filling is set and heated through. If the topping begins to brown too quickly, tent loosely with foil for the last 10 minutes.

Remove from the oven and let rest for 10 minutes before serving. Serve warm directly from the baking dish.